The business of manufacturing and marketing disposable absorbent articles for personal care or hygiene (such as disposable diapers, training pants, adult incontinence undergarments, feminine hygiene products, breast pads, care mats, bibs, wound dressing products, and the like) is relatively capital intensive and highly competitive. To maintain or grow their market share and thereby maintain a successful business, manufacturers of such articles must continually strive to enhance their products in ways that serve to differentiate them from those of their competitors, while at the same time controlling costs so as to enable competitive pricing and the offering to the market of an attractive value-to-price proposition.
One way in which some manufacturers may seek to enhance such products is through enhancements to softness. Parents and caregivers naturally seek to provide as much comfort as they can for their babies, and utilizing products such as disposable diapers that they perceive as relatively soft provides reassurance that they are doing what they can to provide comfort in that context. With respect to other types of disposable absorbent articles that are designed to be applied and/or worn close the skin, an appearance of softness can reassure the wearer or caregiver that the article will be comfortable.
Thus, manufacturers may devote efforts toward enhancing the softness of the various materials used to make such products, such as various web materials, including nonwoven web materials formed from polymer fibers, and laminates thereof, forming the products. Such laminates may include, for example, laminates of polymer films and nonwoven web materials forming the backsheet components of the products.
It is believed that humans' perceptions of softness of a nonwoven web material can be affected by tactile signals, auditory signals and visual signals.
Tactile softness signals may be affected by a variety of the material's features and properties that have effect on its tactile feel, including but not limited to loft, fiber thickness and density, basis weight, microscopic pliability and flexibility of individual fibers, macroscopic pliability and flexibility of the nonwoven web as formed by the fibers, surface friction characteristics, number of loose fibers or free fiber ends, and other features.
Perceptions of softness also may be affected by auditory signals, e.g., whether and to what extent the material makes audible rustling, crinkling or other noises when touched or manipulated.
It is believed that perceptions of softness of a material also may be affected by visual signals, i.e., its visual appearance. It is believed that, if a nonwoven material looks relatively soft to a person, it is much more likely that the person will perceive it as having relative tactile softness as well. Visual impressions of softness may be affected by a variety of features and properties, including but not limited to color, opacity, light reflectivity, refractivity or absorption, apparent thickness/caliper, fiber size and density, and macroscopic physical surface features.
As a result of the complexity of the mix of the above-described characteristics, to the extent softness is considered an attribute of a nonwoven web material, it may elude precise measurement or quantification. Although several methods for measuring and evaluating material features that are believed to affect softness signals have been developed, there are no standard, universally accepted units or methods of measurement for softness. It is a subjective, relative concept, difficult to characterize in an objective way. Because softness is difficult to characterize, it can also be difficult to affect in a predictable way, through changes or adjustments to specifications in materials or manufacturing processes.
Complicating efforts to define and enhance softness is the fact that differing individuals will have differing individual physiological and experiential frames of reference and perceptions concerning what material features and properties will cause them to perceive softness to a lesser or greater extent in a material, and relative other materials.
Various efforts have been made to provide or alter features of nonwoven web materials with the objective of enhancing consumer perceptions of softness. These efforts have included selection and/or manipulation of fiber chemistry, basis weight, loft, fiber density, configuration and size, tinting and/or opacifying, embossing or bonding in various patterns, etc.
For example, one approach to enhancing perceived softness of a nonwoven web has involved simply increasing the basis weight of the web, otherwise manufactured through a spunlaid/spunbond process that includes formation of a batt of loose spun fibers and then consolidating by calender-bonding in a pattern. All other variables remaining constant, increasing the basis weight of such a web will have the effect of increasing the number of fibers per unit surface area, and correspondingly, increasing apparent thickness, fiber density and/or loft. This approach might be deemed effective if the only objective is increasing depth and/or loft signals affecting perceptions of softness, i.e., simply increasing the basis weight of a spunbond nonwoven is one way to increase its depth or loft. However, among the costs involved in producing nonwoven web material formed of polymer fibers is the cost of the polymer resin(s) from which the fibers are spun. Higher basis weight nonwovens require more resin to produce, and therefore, cost more per unit. Thus, attempting to enhance perceived softness by increasing nonwoven basis weight is incompatible with the ever-present objective of controlling or reducing costs.
Another approach has involved forming a nonwoven web of “bicomponent” polymer fibers, by spinning such fibers, laying them to form a batt and then consolidating them by calender-bonding with a pattern, to provide visual effects. Such bicomponent polymer fibers are formed by spinnerets that have two side-by-side sections, that express a first polymer on one side and a second polymer on the other, to form a fiber having a cross section of the first polymer on one side and the second polymer on the other (hence the term “bicomponent”). The respective polymers may be selected so as to have differing melting temperatures and/or expansion-contraction rates. These differing attributes of the two polymers cause the bicomponent fiber products to curl in the spinning process, as they exit the spinnerets and cool. The resulting curled fibers then may be laid down in a batt and calender-bonded in a pattern. It is thought that the curl in the fibers adds loft and fluff to the web, enhancing softness visual and tactile softness signals.
In another approach relating to a backsheet laminate of a film and a non-woven web, prior to lamination with a nonwoven web the film is printed with a subtle pattern which, following lamination with the nonwoven web, is visible therethrough and simulates actual shading that would occur on the nonwoven web surface under various lighting conditions, as if it actually bore a pattern of three-dimensional surface features. The desired effect is to enhance visual softness signals.
Still another approach has involved adding and blending in a white tinting/opacifying agent (for example, titanium dioxide) to the polymer used to form a base layer of fibers forming the nonwoven web, forming the base layer, then forming additional layers by laying down fibers formed of untinted polymer over the base layer, to form a multi-layer batt. Following formation of the multi-layer batt, it is calender-bonded in a pattern, and then subjected to a hydroenhancing or hydroengorgement process to fluff the fibers and increase caliper and loft. It was thought that the presence of untinted, relatively translucent, shiny fibers laid over and interspersed with the base layer of tinted fibers, together with the hydroenhancing/hydroengorgement process, creates visual effects tending to enhance the perception of loft and/or depth. It is also believed that the hydroenhancing/hydroengorgement process actually increases loft and/or caliper, enhancing visual and tactile softness signals.
Still another approach has related to the manner in which products are packaged. Typically, absorbent products such as diapers and feminine hygiene products are packaged in stacked groups. During packaging, the stacks are usually compressed along a direction approximately orthogonal to the major portions of the surfaces formed by nonwovens, such that the caliper and loft of the nonwovens tends to be reduced by compression when packaged. The effect of the compression may subsist after removal of the product from a package, adversely affecting softness signals. Thus, it was thought that reducing the amount of compression in packaging would help to preserve caliper and loft of the nonwovens, and thus preserve the appearance of softness. It will be appreciated, however, that reducing the compression in packaging necessarily has the effect of either reducing the number of products per package, or increasing package size—both of which increase the per-product cost.
The approaches described above have had varying degrees of success, but have left room for improvement in enhancing visual and/or tactile softness signals. Additionally, many current methods for enhancing softness signals in a nonwoven web have the undesirable effect of decreasing desirable mechanical properties such as tensile strength. Generally, it is believed that, for any particular nonwoven web material, processing steps that increase softness signals undesirably decrease strength.